1. Field of the Invention
The present invention relates to a tampering judgement system to judge whether or not a document has been tampered and to an encrypting system for the judgement on tampering and to a method for judging on tampering.
2. Description of the Related Art
Conventionally, when security information is stored, together with public information, in a printing media in which an image representing the public information is printed, for example, following methods are available.
(1) “Security Information Storing Method” Disclosed in Japanese Patent Application Laid-Open No. Hei 9-154007
In technology disclosed in this literature, into dotted public information data being dotted by making binary-coded the security information to be stored is embedded binary-coded information data in a unit pixel according to a predetermined encryption key and the resulting data is used as printing data.
(2) “Security Information Storing Method” Disclosed in Japanese Patent Application Laid-Open No. Hei 9-179494
In technology disclosed in this literature, by making security information to be stored binary-coded, by breaking it into blocks and then by making a content of each block decimal-coded, security information blocks B1, B2, B3, and B4 are created. Moreover, reference information data DS1 is prepared which is obtained by making public information image binary-coded and by embedding a code DR1 representing reference points R1 to R4 into the binary-coded public information image. Then, in a state where one or a plurality of security information blocks is arranged so as to be corresponded to the reference point, codes representing position discriminating marks are embedded into the reference information data DS1 in such a manner that position discriminating marks D1 to D4 matching with predetermined contents or with the security information blocks are printed at a place being apart from the reference point marks by one or two dimensional distances matching with contents of a security information block and the resulting data is used as printing data.
When a printed content is a resident card, certificate of a resident seal impression, receipt, or a like and when the printing media is ordinary paper, there is possibly fraud that characters such as a name, address, money amount, date, or a like are erased using an amending liquid or a like and are overwritten with characters with same fonts as used in printing or that characters are added to handwritten characters representing a money amount which is submitted as a formal document. However, an aim of the conventional technology disclosed above is to embed security information into an object to be printed and public information itself cannot be protected. That is, if the object to be printed is tampered, it is difficult to detect such tampering. Moreover, when information to be embedded into an object to be printed is matched to a content of public information or when information to be embedded is associated with a content of public information, checking as to whether or not the content has been tampered is possible, however, a problem occurs that, in order to automatically perform such the checking, a mechanism in which a content of public information can be recognized by a machine such as an OCR (Optical Character Reader) is required on a side of a party making such the checking, which causes a scale of a system to become larger.